Lift truck

ABSTRACT

A load-lifting apparatus comprising a base, a pair of stationary uprights, a pair of extensible uprights, a load carriage and pairs of upper, middle and lower guide rollers positioned between said uprights and/or between said uprights and said load carriage, said upper and lower rollers cooperating with their respective uprights to resist the forward thrust caused by the load, said middle and lower rollers cooperating with their respective uprights to resist the side thrust caused by eccentric loading.

United States Patent Akibumi Shinoda Chita-gun, Aichi-ken;

Goro Nishi, Chita-gun, Aichi-ken, Japan 771,963

Oct. 30, 1968 Jan. 19, 1971 Toyoda Automatic Loom Works Ltd. Toyoda-cho,Kariya-shi, Aichi-ken, Japan Nov. 7, 1967, Dec. 14, 1967 Japan Nos.42/71555 and 42/80227 inventors Appl. No. Filed Patented AssigneePriority LIFT TRUCK 11 Claims, 14 Drawing Figs.

US. Cl 187/9, 187/95 Int. Cl 1366b 9/20 [50] Field ofSearch 187/9, 195;2l4/(lnquired); 52/(lnquired) [56] References Cited UNYTED STATESPATENTS 3,358,791 12/1967 Goodacre 187/9 Primary Examiner-Harvey C.Hornsby Attorney-Blum, Moscovitz, Friedman, Blum & Kaplan ABSTRACT: Aload-lifting apparatus comprising a base, a pair of at a uprights, a P rfes e ibls upri hts a lea carriage and pairs of upper, middle and lowerguide rollers positioned between said uprights and/or between saiduprights and said load carriage, said upper and lower rollerscooperating with their respective uprights to resist the forward thrustcaused by the load, said middle and lower rollers cooperating with theirrespective uprights to resist the side thrust caused by eccentricloading.

PATENIED JAN] 9197: I 3' 556' 247 sum 2 BF 5 PATENTED JAN 1 9191.

saw u or 5 LIFI'TRUCK I BACKGROUND or TI-IIE'INVENTION This inventionrelates generally to load-lifting apparatus for handling goods and morespecifically-to the lift truck type of such apparatus utilized forelevating, storing and transporting desired load materials. Lifts'tucksgenerally include a structure of uprights and a load carriage.Theconventionaluprights generally consists of a pair of stationary,laterally spaced uprights disposed in facing relation and fixed to theforward end portion of the industrial lift truck, and a pair oflaterally s ed extensible upri hts disposed between said stationa I S WMore particularly, said upper, middle and lower rollers are mounted onstub shafts which lie -'in substantially the same plane and extend in adirection normal to the longitudinal axis of the load carriage. Theuprights are formed with a curved surface in the inside corner definedby the rearward flange and web thereof and a supporting surface incontinuation of said curved surface on a portion of the inner surface ofsaid web. Said curved and supporting surfaces'extend downwardly alongsaid inside corner from a point a predetermined length from the upperend of said uprights. A second curved surface is pr0- vided in the otherof said upright inside corners and a second supporting surface isprovided in continuation of said second curved surface along a portionof said web, said second curved and supporting surfaces extendingupwardly substantially from said point located a predetermined distancefrom the upper end of said uprights.

Along most of the length of the uprights, the upper rollers engage theforward flange thereof, and,'in conjunction with the lower rollers,which engage the rearward flange and the adjacent first-mentioned curvedand supporting surfaces to resist the forward driving force on the loadcarriage and uprights rollers. Said upper and lower rollers arehorizontally supported on stub shafts extending in a direction normal tothe longitudinalaxis of the truck and rotatecontacting, respectively,the forward and rearward flanges of said extensible uprights; The siderollers, of which there are two pairs, are

disposed between said upper and lower rollers. Said side rollers aredisposed in planes substantially perpendicular to the planes of saidupper and lower rollers and rotate contacting the webs ofsaid'extensible uprights.

However, it has been found that this arrangement is not satisfactorysince it requires a" large number of rollers and complicated adjustmentsof the position of the side rollers, In order to overcome this problem,it has been proposed that the upper and lower rollers of theloadcarriage which rotate relative to the extensible uprights be tilted inopposite directions against the web of the uprights, whereby the treadof said upper andlower rollers respectively contacts against the insidecorner angles defined by the forward and rearward flanges and the web ofsaid uprights; In this manner, the side rollers can be omitted. However,the force applied by the upper rollers against the inside corner angledefined by said forward flange and web has a substantial lateralcomponent tending to force the extensible uprights apart. While suchlaterally applied force is present in all upright structures, it isparticularly significant in the foregoing arrangement due to when theload carriage moves longitudinally, The middle rollers contact saidfirstmentioned supporting surface and in conjunction with the lowerrollers resist the lateral thrust force. When the load carriage israised so that the upper rollers are projected from the upper end of theextensible uprights, the middle rollers transfer to the forward flangeand said second curved and supporting surfaces adjacent thereto, wherebymiddle and lower rollers resist both the forward and lateral thrustforces on the load carriage and uprights. TI-ie portions of said iprightwebs not having said first-mentioned and second supporting surfacesformed thereon are recessed to limit the friction between the rollersand said uprights.

In a further embodiment of the invention, three pairs of rol lerscorresponding to the upper,-middle and lower rollers described above areprovided between the extensible and stasubstantially eliminated byconcentrating said lateral force at the structure of the uprights. Theextensible uprights are generally connected on the outer surface oftheir rearward flanges and because of structural limitations, theconnecting beams of said extensible uprights are generally weaker thanthe corresponding beams interconnecting the stationary uprights. Sincethe lateral forces in the foregoing arrangement are applied at theinside comer angle defined by the forward flange and the web, the momentof said lateral forces is sub- .stantiallyincreased whereby the strain'on the beams connects ing the rearward flanges of theextensibleuprights is substantially increased. For this reason, theabove-described arrangement is subject to failure under high eccentricloads, and is therefore not a suitable solution to the problempresented.

7 SUMMARY or THE llNVENTlON Generally speaking, and in accordance withthe invention, a load-lifting apparatus having pairs of upper, middleand lower guide rollers positioned between the uprights and the loadcarriage is provided, said upper and lower rollers cooperating withtheir respective uprights to resist the forward thrust part be obviousand will in part be apparent from the specificaused by the load, saidmiddle and lower rollers cooperating with their respective uprights toresist the side or lateralthrust caused by eccentric loading. Further,said middle rollers, in cooperation withtheir respective uprights, alsoassume the function of resisting the forward thrust when the loadcarriage is elevated to the region wherein the upper rollers projectabove said uprights,

cation. v

The invention accordingly comprises the features of construction,constructions of elements, and arrangement of parts which will beexemplified in the constructions herein after set forth, and the scopeof the invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawings, in which:

FIG. 1 is a perspective view of a lift truck provided with theload-lifting apparatus according to the invention;

FIG. 2 is a side elevational view of the load-lifting apparatus of FIG.1 with the load carriage raised to its uppermost position;

FIG. 3. is an exploded side elevational view of the upper portion of theload-lifting apparatus of FIG. 2 with the load carriage slightlylowered;

FIG. 4 is a top plan view ofthe load-lifting apparatus of FIG. 3;

FIG. 5 is a partial sectional view of the load carriage, rollers andextensible uprights ofthe load-lifting apparatus of FIG. 3;

FIGS. 6, 7 and 8 are cross sectional views taken across horizontalplanes of the upper, middle and lower rollers respectively and theassociated extensible uprights as disposed in FIG. 1;

FIGS. 9, 10 and 11 are cross sectional views taking along horizontalplanes of the upper, middle and lower rollers respectively and theassociated extensible uprights, as disposed in FIG. 2; and

FIGS. 12, 13 and 14 are cross-sectional views taken along horizontalplanes of the upper, middle and lower rollers respectively disposedbetween corresponding stationary and extensible uprights.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, theload-lifting apparatus according to the invention includes a pair ofstationary uprights 1 laterally spaced and facing each other at thefront portion of a lift truck. The stationary uprights 1 are ofchannel-shaped cross section, and, as shown in FIG. 4, are firmly bracedtogether with the open channels in facing relation by lateral beams 2, 3and 4 disposed at the lower end portion, the middle portion and theupper end portion thereof respectively. As well known in the art, thestationary uprights 1 can be tilted back and forth by means of tiltingcylinders 6 secured at one end to the side frame of the lift tuck and atthe other end to lateral beam 3. Connecting portions 5 which extend fromthe back of lateral beam 2 serve as the fulcrum for the tilting of saidstationary uprights.

A pair of laterally spaced extensible uprights 7 are provided betweenstationary uprights 1. Said extensible uprights may be channel-shaped orI-shaped and are disposed with the channels thereof in facing relation.Said extensible uprights are displaceable longitudinally alongstationary uprights 1 and are supported in relation thereto by means oftwo pair of rollers 8 and 10. As shown in FIGS. 2 and 4, the upper endportions of the back surface of extensible uprights 7 are bracedtogether by a relatively strong lateral beam 11, while the middle andlower end portions thereof are braced together by relatively thin andweak lateral beams 12 and 13. The strength of the latter two lateralbeams is limited by the fact that they must pass lateral beams 3 and 4as the extensible uprights are raised and lowered, while notinterferring with other parts of the load-lifting apparatus. The latterlimitations do not apply to the top most lateral beam 11.

The lifting device of the present invention has a load carriage 14disposed on the front side of uprights 1 and 7. Said load carriageincludes the conventional structures such as finger bars 15, forks 16mounted on said finger bars and a pair of brackets 17 extendingbackwards from said finger bars between extensible uprights 7. As shownin FIGS. 5 8, brackets 17 have pairs of stub shafts 18, 19 and 20extending respectively from the uppermost portion, the portion slightlybelow said uppermost portion, and the lowermost portion thereof. Saidsub shafts extend horizontally from brackets 17 in substantially thesame plane, said plane being substantially perpendicular to the plane ofthe longitudinal axis of the truck. Mounted on stub shafts 18, 19 and 20respectively are upper rollers 21, middle rollers 22 and lower rollers23, which are disposed within the channels of extensible uprights 7whereby the load carriage 14 can move in the longitudinal directionrelative to said uprights. The spacing between said rollers can beoptionally selected in accordance with the design objects of thespecific embodiment.

As shown in FIGS. 6 8, the channel of each of the extensible uprights 7along which the rollers ride, is formed by forward flange 7a andrearward flange 7b which extend from the web thereof. Curved rollingsurface 7c is formed at the inside corner defined by the intersection ofthe rearward flange 7a and the web. Said curved surfacehas the sameradius ofcurvature as the front end periphery of the respective rollers.Supporting surface 7d is formed on the web in continuation of the curvedsurface and defines a right angle or a slightly oblique angle withrearward flange b. The remaining internal surface of the web is recessedto define an escape surface 72 of the web and space 24 between said weband the forward end ofthe respective rollers.

The lateral movement of the upper rollers 21, mounted on stub shaft 18.is restricted and the forward end thereof is prevented from contactingthe supporting surface 7d of said extensible uprights by means ofretaining ring 25. On the other hand, the lower rollers 23, mounted onstub shafts 20, are adjusted and displaced laterally by an appropriatenumber of shims 26 inserted on said shaft so that the forward ends ofthe outer periphery thereof contact the curved surface 70 of extensibleuprights 7. The middle rollers 22, mounted on stub shaft 19 are ofasmaller diameter than upper rollers 21 so that the outer peripheralsurface thereof is prevented from contacting forward flange 7a,even whensaid upper rollers are in contact with said forward flange. The lateralposition along stub shafts 18 of said upper rollers is adjusted by thesame means as lower rollers 23 so that the forward end of the side facethereof contacts supporting surface 711 of said extensible uprights.Thus, when the load carriage is disposed as shown in FIGS. 1 and 6 -8,and the fork 16 is loaded, the outer peripheral surface of the upperrollers 21 is press-contacted against forward flange 711 while the outerperipheral surface of lower rollers 23 press-contacted against rearwardflange 7b to resist mainly against the forward bending load. When sodisposed, middle rollers 22 are completely free from the forward drivingforce but, when an eccentric load is applied to load carriage 14, themiddle roller 22 associated with one of said extensible uprights and thelower roller 23 associated to the other of said extensible uprightscooperate to resist the lateral thrust force resulting from saideccentric load.

A further feature of the load lifting apparatus according to theinvention, shown in FIGS. 3 and 9 11 rests in rolling curved surface 7cand supporting surface 711 which do not extend over the entire length ofextensible uprights 7, but rather, extend downwardly only from a point apredetermined length from the upper end of said extensible uprights.Thus, the portion of the web of said extensible uprights above thecutoff point of said curved and supporting surfaces is recessed in thesame manner as the central portion of the web. A second curved rollingsurface 7c is formed in the inside corner angle defined by the forwardflange 7a and web of extensible uprights 7 while a second supportingsurface 7d is formed on a portion of said web in continuation of saidsecond curved surface. As shown in FIG. 3, said second curved andsupporting surfaces extend upwardly substantially from the upper cutoffpoint of the first mentioned curved and supporting surfaces 7c and 7d.The second supporting surface 7d defines a right angle or a slightlyobtuse angle with forward flange 70. Thus, except for the portions onwhich supporting surfaces 7d and 7d are formed, the web of saidextensible uprights is recessed. If extensible uprights 7 are formed bya drawing process, second curved and supporting surfaces 7c and 7d arepreferably separately formed and secured on the escape surface 7e of theweb of said uprights. As shown in FIGS. 9 -ll, first-mentionedsupporting surface 7d extends a greater distance from the recessedescape surface 7e of the web than does second supporting surface 7d forreasons that will be explained below.

As seen in FIG. 2, when load carriage 14 is elevated to its uppermostposition, upper rollers 21 project above the upper end of extensibleuprights 7. The above described arrangement permits middle rollers 22 toassume the function of resisting the forward thrust of the load normallyperformed by upper rollers 21 when the latter rollers extend above andare out of engagement with the extensible uprights. Specifically, whenupper roller 21 is raised to a level where it no longer contacts forwardflange 7a of said extensible uprights, the outer peripheral surface ofmiddle rollers 22 is press-contacted against and rotates on said forwardflange in place of said upper rollersJMiddle rollers 22 are of adiameter slightly smaller than that of upper rollers 21' and normally donot engage forward flange 7a. As seen in FIG. 10, in this area ofoperation, middle rollers 22 also engage second curved and supportingsurfaces 70' and 7d.

.The actual operating conditions of each roller of the loadliftingapparatus according to the invention, as load carriage 14 is elevated,is as follows. When the load carriage is disposed as shown in FIG. 1 andis being raised,both upper rollers 21 are in engagement with forwardflange 7a and rotate in the clockwise direction (FIG. 3), while bothlower rollers 23 engage rearward flange7b, curved rolling surface 7 cand supporting surface 7d and rotate in the counterclockwise direction(FIG. 3). The middle roller 22 on the side of load carriage 14 on whichthe eccentric load is placed contacts supporting surface 7d and rotatesin the counterclockwise direction. The other middle roller 22, which ison the side of load carriage 14 on which the eccentric load is notplaced, does not contact any surface of the adjacent extensible upright7 and is stationary. Thus, in this region of operation, only one of saidmiddle rollers rotates to resist the application of eccen tric load inconjunction with the lower roller 23 disposed on the other side of thecarriage.

When load carriage 14 is elevated and approaches the uppermost position,the curved rolling surface 70 and supporting surface 7d of extensibleuprights 7 come to an end, and the middle roller 22, which resisted thelateral driving force due to an eccentric load by engaging supportingsurface 7d then contacts supporting surface 7d adjacent the forwardflange and the rotating direction thereof is reversed into the clockwisedirection (FIG. 3). In operation, the middle roller gradually reducesits contact with supporting surface 7d as it rotates upwardly. Ofcourse, if the outer peripheral side face of said middle roller were tosimultaneously contact both supporting surface 7d and supporting surface7d the roller would be prevented from smoothly rotating and asubstantial frictional resistance would be interposed into the system.This problem is minimized and the transition between supporting surfacesis rendered relatively smooth by forming supporting surface 711' so thatit extends from escape surface 7e of the web a lessor distance thansupporting surface 7d, as described above.

Thus, as the load carriage is raised, one of said middle rollers ispress-contacted against supporting surface 7d adjacent the forwardflange and the direction of rotation thereof is reversed. When upperrollers 21 are projected above the upper end of extensible uprights 7,the outer peripheral surface of both middle rollers 22 engage forwardflange 7a and curved rolling surface 7c, thereby enabling said middlerollers to resist both the lateral and forward directed load incooperation with the lower rollers 23. As the middle rollers 22 arepress-contacted to the curved surface 7c disposed in the inside comerangle defined by the forward flange and web, the interval between therollers is shortened. [t is noted that the moment of the lateral force,which tends to expand extensible uprights 7 is slightly increased inthis region, since it is applied adjacent the forward flange of theextensible uprights, this in crease is present only when the loadcarriage is elevated to the region of its uppermost position. in thisregion, the increased moment can be supported by the upper lateral beam11 of the extensible uprights 7 which can be preferably strengthenedsince the size thereof is not restricted by connecting beams 3 and 4 ofstationary uprights 1.

Referring now to FIGS. 12 -14, portions of a further embodiment of theload-lifting apparatus according to the invention is shown, wherein theroller arrangement according to the invention is applied'to support theextensible uprights 7 on stationary uprights 1. Thus, three pairs ofrollers, namely upper rollers 8, middle rollers 59 and lower rollers aremounted on the outer surface of the web of extensible uprights 7 and areadapted to ride in the adjacent channel of the respective stationaryuprights I. Said stationary upright channels correspond in structure tothe extensible upright channels described above and rollers 8, 9 and 10cooperate with said stationary upright channel and function in the samemanner as rollers 21, 22 and 23 described above. Rollers 8, 9 and 10 mayalso be provided between the first and second extensible uprights in anassembly of three pairs of uprights. In any event, all of said rollersare disposed in substantially parallel planes at the lower portion ofthe extensible uprights which support said rollers.

As shown in FIGS. 1 and 4, load carriage l4 and extensible uprights 7are operated through a pair of chains 27 and a conventional hydraulicmechanism 28. Said hydraulic mechanism is vertically secured on lateralbeam 4 of the stationary uprights for the longitudinal displacement ofextensible uprights 7 and load carriage 14. The head member 29 of saidhydraulic mechanism is secured to the upper end of the longitudinallyextensible piston rod and supports a pair of sprockets and chains 27,one end thereof being fixed on the hydraulic mechanism and the other endthereof being fixed on the load carriage 14 through said sprockets.

From the foregoing description, it is apparent that the rollerarrangement of the load-lifting apparatus according to the invention isextremely simple in construction and easily adjusted. Said apparatusdoes not require the side rollers utilized in conventional arrangements.Further, through most of its range of operation, the lateral thrustforce working through the middle and lower rollers is concentrated onthe inside comer defined by the rearward flange and web of the extensible uprights or the supporting surface adjacent thereto so that themoment of the force tending to expand the extensible uprights sideway issubstantially reduced.

Still a further advantage of the arrangement according to the inventionrests in the use of the middle rollers to assume the function ofresisting the forward thrust of the load when the upper rollers projectbeyond the upper end of the rollers. In this manner, the lifting heightof a lift truck can be increased without changing the total height ofthe truck. Thus where rollers in accordance with the invention aredisposed between the load carriage and the uprights and/or between thestationary and extensible uprights, the lifting height of the lift truckis increased by the distance between the upper and middle rollers.

lt will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above constructions withoutdeparting from the spirit and scope of the invention, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

lt is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

We claim:

1. A load-lifting apparatus comprising a base; a pair of laterallyspaced-apart uprights beingvbraced together by a lateral beam at theirback surfaces and mounted on said base; a movable member adapted forlongitudinal movement with respect to said uprights for lifting theload; and pairs of upper rollers, middle rollers and lower rollerspositioned between said uprights and movable member and supported bysaid movable member for guiding the movement of said movable member,each of said uprights having a web, forward and rearward flangesextending inwardly from said web, a curved surpairs of rollers beingdisposed between the forward and rear ward flange of each of saiduprights, all of said rollers being rotatable in substantially parallelplanes, said pair of upper rollers being in contact with said forwardflanges, each of said middle rollers having a side face adapted toengage the adjacent supporting surface in response to an eccentric load,said lower rollers engaging said rearward flanges, curved surfaces andsupporting surfaces, whereby said upper and lower rollers cooperate toresist the forward thrust of said load, and one of said lower rollersengaging one of said uprights cooperates with one of said middle rollersengaging the other of said uprights to resist the side thrust andsubstantially eliminating twisting moment applied to the uprightsresulting from an eccentric load.

2, A load-lifting apparatus as recited in claim 1 wherein the portion ofsaid webs between said supporting surface and said forward flange isrecessed away from said rollers to decrease contact resistance betweensaid rollers and said uprights.

3. A loadlifting apparatus as recited in claim 2 wherein said uprightsare stationary with respect to said base, said movable member being aload carriage mounted for longitudinal movement with respect to saidstationary uprights for lifting load, said rollers being positionedbetween said uprights and said load carriage.

4. A loadlifting apparatus as recited in claim 2 wherein said uprightsare stationary with respect to said base, said movable member includinga pair of laterally spaced extensible uprights longitudinally movablewith respect to said stationary uprights for lifting load, said rollersbeing positioned between said stationary uprights and said extensibleuprights.

5. A load-lifting apparatus as recited in claim 2 wherein said uprightsare longitudinally extensible with respect to said base, said movablemember including a load carriage mounted on said extensible uprights andlongitudinally movable with respect thereto for lifting load, saidrollers being positioned between said extensible uprights and said loadcarriage.

6. A load-lifting apparatus as recited in claim 2 wherein said uprightsare stationary with respect to said base, said movable member includinga pair of laterally spaced extensible uprights longitudinaliy movablewith respect to said stationary uprights, a load carriage mounted onsaid extensible uprights for longitudinal movement with respect theretofor lifting load, and a second set of rollers including pairs of upper,middle and lower rollers positioned between said extensible uprights andsaid load carriage, said first-mentioned rollers being positionedbetween said stationary uprights and said extensible uprights, each ofsaid extensible uprights having a web, forward and rearward flangesextending inwardly from said web, a curved surface formed in the insidecorner defined by said rearward flange and web, and a supporting surfaceformed in continuation of said curved surface on a portion of the innersurface of said web, all of said second set of rollers being rotatablein substantially parallel planes, said second pair of upper rollersengaging said extensible upright forward flanges, each of said secondpair of middle rollers having a side face engageable with the adjacentextensible upright supporting surfaces, said second pair of lowerrollers engaging said extensible upright rearward flanges and'curved andsupporting surface, the portion of said extensible upright websextending between said supporting surface and said forward flange beingrecessed away from said rollersv 7. A load-lifting apparatus as recitedin claim 2, wherein said upright curved and supporting surfaces extenddownwardly only from a point a predetermined distance from the top ofsaid uprights, said middle rollers engaging said forward flanges whensaid upper rollers project above the upper end of said up ights, wherebysaid middle and lower rollers cooperate to resist the forward thrust ofsaid load when said upper rollers projtct above the upper end of saiduprights.

8. A load-lifting apparatus as recited in claim 7, wherein each of saiduprights is formed with a second supporting surface adjacent saidforward flange, the portion of said webs extending between said secondsupporting surface and said rearward flange being recessed away fromsaid rollers, said second suppo ting surfaces extending upwardlysubstantially from said point located at a predetermined length from thetop of said uprights, each of said middle rollers having a side faceadapted to engage the adjacent second supporting surface in response toan eccentric road when said upper rollers project above the upper end ofsaid uprights, whereby one of said lower rollers engaging one of saiduprights cooperates with one of said middle rollers engaging the otherof said uprights to resist the side thrust resulting from an eccentricload when said upper rollers project above the upper end of saiduprights.

9. A load-lifting apparatus as recited in claim 8, each of said uprightshaving a second curved surface formed in the inside corner defined bysaid forward flange and web, said second supporting surface being formedin continuation of said second curved surface.

it). A load-lifting apparatus as recited in claim 8, wherein saidfirst-mentioned supporting surface extends from said web towards saidrollers a greater distance than said second supporting surface wherebycontact with both of said supporting surfaces by said middle rollers isminimized.

iii. A load-lifting apparatus as recited in claim ll, wherein saidcurved and supporting surfaces extend downwardly along said uprightsonly from a point a predetermined length from the top of said uprights,each of said uprights having a second supporting surface formed on aportion of the inner surface of said web adjacent said forward flange,said first-mentioned supporting surface projecting from said web towardsaid rollers a distance greater than said second supporting surface, theportions of said web aside from the portions having said firstmentionedand second supporting surfaces thereon being recessed away from saidrollers, each of said middle rollers being engageable against saidforward flange and second supporting surface of its respective uprightwhen said upper rollers project from the upper end of said uprights,whereby said middle rollers cooperate with said lower rollers to resistthe forward and lateral thrust of said load when said upper rollersproject from the upper end of said uprights.

1. A load-lifting apparatus comprising a base; a pair of laterallyspaced-apart uprights being braced together by a lateral beam at theirback surfaces and mounted on said base; a movable member adapted forlongitudinal movement with respect to said uprights for lifting theload; and pairs of upper rollers, middle rollers and lower rollerspositioned between said uprights and movable member and supported bysaid movable member for guiding the movement of said movable member,each of said uprights having a web, forward and rearward flangesextending inwardly from said web, a curved surface formed in the insidecorner defined by said rearward flange and said web, and a supportingsurface formed in continuation of said curved surface on a portion ofthe inner surface of said web, one of each of said upper, middle andlower pairs of rollers being disposed between the forward and rearwardflange of each of said uprights, all of said rollers being rotatable insubstantially parallel planes, said pair of upper rollers being incontact with said forward flanges, each of said middle rollers having aside face adapted to engage the adjacent supporting surface in responseto an eccentric load, said lower rollers engaging said rearward flanges,curved surfaces and supporting surfaces, whereby said upper and lowerrollers cooperate to resist the forward thrust of said load, and one ofsaid lower rollers engaging one of said uprights cooperates with one ofsaid middle rollers engaging the other of said uprights to resist theside thrust and substantially eliminating twisting moment applied to theuprights resulting from an eccentric load.
 2. A load-lifting apparatusas recited in claim 1 wherein the portion of said webs between saidsupporting surface and said forward flange is recessed away from saidrollers to decrease contact resistance between said rollers and saiduprights.
 3. A load-lifting apparatus as recited in claim 2 wherein saiduprights are stationary with respect to said base, said movable memberbeing a load carriage mounted for longitudinal movement with respect tosaid stationary uprights for lifting load, said rollers being positionedbetween said uprights and said load carriage.
 4. A load-liftingapparatus as recited iN claim 2 wherein said uprights are stationarywith respect to said base, said movable member including a pair oflaterally spaced extensible uprights longitudinally movable with respectto said stationary uprights for lifting load, said rollers beingpositioned between said stationary uprights and said extensibleuprights.
 5. A load-lifting apparatus as recited in claim 2 wherein saiduprights are longitudinally extensible with respect to said base, saidmovable member including a load carriage mounted on said extensibleuprights and longitudinally movable with respect thereto for liftingload, said rollers being positioned between said extensible uprights andsaid load carriage.
 6. A load-lifting apparatus as recited in claim 2wherein said uprights are stationary with respect to said base, saidmovable member including a pair of laterally spaced extensible uprightslongitudinally movable with respect to said stationary uprights, a loadcarriage mounted on said extensible uprights for longitudinal movementwith respect thereto for lifting load, and a second set of rollersincluding pairs of upper, middle and lower rollers positioned betweensaid extensible uprights and said load carriage, said first-mentionedrollers being positioned between said stationary uprights and saidextensible uprights, each of said extensible uprights having a web,forward and rearward flanges extending inwardly from said web, a curvedsurface formed in the inside corner defined by said rearward flange andweb, and a supporting surface formed in continuation of said curvedsurface on a portion of the inner surface of said web, all of saidsecond set of rollers being rotatable in substantially parallel planes,said second pair of upper rollers engaging said extensible uprightforward flanges, each of said second pair of middle rollers having aside face engageable with the adjacent extensible upright supportingsurfaces, said second pair of lower rollers engaging said extensibleupright rearward flanges and curved and supporting surface, the portionof said extensible upright webs extending between said supportingsurface and said forward flange being recessed away from said rollers.7. A load-lifting apparatus as recited in claim 2, wherein said uprightcurved and supporting surfaces extend downwardly only from a point apredetermined distance from the top of said uprights, said middlerollers engaging said forward flanges when said upper rollers projectabove the upper end of said uprights, whereby said middle and lowerrollers cooperate to resist the forward thrust of said load when saidupper rollers project above the upper end of said uprights.
 8. Aload-lifting apparatus as recited in claim 7, wherein each of saiduprights is formed with a second supporting surface adjacent saidforward flange, the portion of said webs extending between said secondsupporting surface and said rearward flange being recessed away fromsaid rollers, said second supporting surfaces extending upwardlysubstantially from said point located at a predetermined length from thetop of said uprights, each of said middle rollers having a side faceadapted to engage the adjacent second supporting surface in response toan eccentric load when said upper rollers project above the upper end ofsaid uprights, whereby one of said lower rollers engaging one of saiduprights cooperates with one of said middle rollers engaging the otherof said uprights to resist the side thrust resulting from an eccentricload when said upper rollers project above the upper end of saiduprights.
 9. A load-lifting apparatus as recited in claim 8, each ofsaid uprights having a second curved surface formed in the inside cornerdefined by said forward flange and web, said second supporting surfacebeing formed in continuation of said second curved surface.
 10. Aload-lifting apparatus as recited in claim 8, wherein saidfirst-mentioned supporting surface extends from said web towards saidrollers a greater distance than said secoNd supporting surface wherebycontact with both of said supporting surfaces by said middle rollers isminimized.
 11. A load-lifting apparatus as recited in claim 1, whereinsaid curved and supporting surfaces extend downwardly along saiduprights only from a point a predetermined length from the top of saiduprights, each of said uprights having a second supporting surfaceformed on a portion of the inner surface of said web adjacent saidforward flange, said first-mentioned supporting surface projecting fromsaid web toward said rollers a distance greater than said secondsupporting surface, the portions of said web aside from the portionshaving said first-mentioned and second supporting surfaces thereon beingrecessed away from said rollers, each of said middle rollers beingengageable against said forward flange and second supporting surface ofits respective upright when said upper rollers project from the upperend of said uprights, whereby said middle rollers cooperate with saidlower rollers to resist the forward and lateral thrust of said load whensaid upper rollers project from the upper end of said uprights.